You may have hit CMD I and inverted the colors. Move your cursor over the image and see review the values in the info palette.
If they are reading correctly to what you see on the screen your image is altered and posisbly doing an invert again would restore you.
If the colors are reading opposite, then you have some sort of display issue.
No, it was not any of these ;-) Using Photoshop since a decade.. :-) But thanks for the suggestion.
To give more information: Several layers are changed, not every layer - it seems as if information was lost/altered while saving - the file looks distorted with image information that has not been there in the beginning.
Did you ever figure out what was going on, because the same thing happened to me two days ago and I've been struggling with it since, it's a pain in the *** to go over each layer and see if something is messed up!